When two natural bodies of water stand at different levels, building a canal between them presents a complicated engineering problem.
(A)
Then the upper gates open and the ship passes through. For downstream passage, the process works the opposite way. The ship enters the lock from the upper level, and water is pumped from the lock until the ship is in line with the lower level.
(B)
When a vessel is going upstream, the upper gates stay closed as the ship enters the lock at the lower water level. The downstream gates are then closed and more water is pumped into the basin. The rising water lifts the vessel to the level of the upper body of water.
(C)
To make up for the difference in level, engineers build one or more water “steps,” called locks, that carry ships or boats up or down between the two levels. A lock is an artificial water basin. It has a long rectangular shape with concrete walls and a pair of gates at each end.
* rectangular: 직사각형의
